In the spinning industry it is well-known that before obtaining the desired quality of thread that a given method of production can provide, it is often desirable to subject the thread, at a certain stage in its manufacture, to a chemical treatment, for example by causing it to pass into a suitable bath. For this purpose, the thread to be treated is unwound from a first bobbin, is passed into the treatment bath and is then rewound on a finishing bobbin. The thread is moved between the first and finishing bobbins by an off-winding apparatus disposed in the path of travel of the thread and generally between the treatment bath and the finishing bobbin.
Three problems arise when using an off-winding apparatus:
(1) it is necessary to start up the entire system at a progressively increasing speed to avoid breaking the thread;
(2) rapid braking is necessary, since it serves no purpose to allow the apparatus to continue to operate after the feed bobbin is empty; and
(3) off-winding of the thread has to be carried out at a constant speed, even though the outside diameter of the thread wound on the bobbins varies during the operation, since it is necessary that each feed portion of the thread should dwell for the same length of time in the treatment bath. Furthermore a sudden change in the off-winding speed of the thread could cause it to be broken.
There is however a trend towards the use of off-winding apparatuses which operate at progressively increasing speeds for the purpose of reducing the time needed for an operation. In the case of off-winding apparatuses operating at off-winding speeds above 1000 meters/minute, it becomes impossible to use purely mechanical means such as variable-speed motors, which may operate satisfactorily on a permanent basis at relatively low off-winding speeds, in the order of 500 meters/minute, but which cannot be used at high speeds, in the order of 1000 meters/minute, and which also do not operate during changeover, that is to say during the start-up and braking stages, which are the most delicate stages of the operation.
An object of the present invention is to avoid these disadvantages by providing a regulable and controlled high-speed off-winding apparatus which enables gradual start-up to be achieved so as to avoid thread breakage which occurs when start-up is too sudden.
Another object of the present invention is to provide a braking system having two positions, namely one for rapid stopping and one in which the apparatus is maintained in the stopped position for enabling manual operations to be carried out.
Another object of the present invention is to provide an electronic control circuit for a clutch-brake arrangement.